Codec and Bandwidth (2/2)

Codec and Bandwidth

This seems quite bandwidth-inefficient as each subsequent 10 byte speech payload comes
with a dedicated overhead. To solve the problem, more than one speech frame needs be
transmitted per IP packet.

How can we increase the payload per Ethernet frame?
Let's try to pack 2 frames of speech information at 10 ms coming out of a G.729 codec and
calculate the resulting bandwidth. 66 bytes of overhead are responsible for 2 x 10 ms of
payload hence 86 bytes per frame or 688 bits. As two 10 ms speech frames are carried the
resulting amount of packets per second has to be divided by 2. This gives us 50 packets.
50 packets per second at 688 bits correspond to a bit rate of 34 kbps or 68 kbps for the full
duplex line capacity. Thus, a significant bandwidth reduction of 50% has been achieved.